Delayed linear dimensional changes of five high strength gypsum products used for the fabrication of definitive casts

An in vitro comparison of the dimensional stability of four 3D-printed models under various storage conditions

OBJECTIVES

To investigate the dimensional stability of various 3D-printed models derived from resin and plant-based, biodegradable plastics (PLA) under specific storage conditions for a period of up to 21 weeks.

MATERIALS AND METHODS

Four different printing materials, including Draft V2, study model 2, and Ortho model OD01 resins as well as PLA mineral, were evaluated over a 21-week period. Eighty 3D-printed models were divided equally into two groups, with one group stored in darkness and the other exposed to daylight. All models were stored at a constant room temperature (20°C). Measurements were taken at 7-week intervals using the Inspect 3D module in OnyxCeph software (Image Instruments GmbH, Chemnitz, Germany).

RESULTS

Dimensional change was noted for all of the models with shrinkage of up to 0.26 mm over the study period. Most contraction occured from baseline to T1, although significant further contraction also arose from T1 to T2 (P < .001) and T1 to T3 (P < .001). More shrinkage was observed when exposed to daylight overall and for each resin type (P < .01). The least shrinkage was noted with Ortho model OD01 resin (0.16 mm, SD = 0.06), and the highest level of shrinkage was observed for Draft V2 resin (0.23 mm, SD = 0.06; P < .001).

CONCLUSIONS

Shrinkage of 3D-printed models is pervasive, arising regardless of the material used (PLA or resin) and being independent of the brand or storage conditions. Consequently, immediate utilization of 3D printing for orthodontic appliance purposes may be preferable, with prolonged storage risking the manufacture of inaccurate orthodontic retainers and appliances.

Accuracy of maximum intercuspal position located by using four intraoral scanners and an artificial intelligence-based program

STATEMENT OF PROBLEM

Maxillary and mandibular scans can be articulated in maximum intercuspal position (MIP) by using an artificial intelligence (AI) based program; however, the accuracy of the AI-based program locating the MIP relationship is unknown.

PURPOSE

The purpose of the present clinical study was to assess the accuracy of the MIP relationship located by using 4 intraoral scanners (IOSs) and an AI-based program.

MATERIAL AND METHODS

Conventional casts of a participant mounted on an articulator in MIP were digitized (T710). Four groups were created based on the IOS used to record a maxillary and mandibular scan of the participant: TRIOS4, iTero, i700, and PrimeScan. Each pair of nonarticulated scans were duplicated 20 times. Three subgroups were created: IOS, AI-articulated, and AI-IOS-corrected subgroups (n=10). In the IOS-subgroup, 10 duplicated scans were articulated in MIP by using a bilateral occlusal record. In the AI-articulated subgroup, the remaining 10 duplicated scans were articulated in MIP by using an AI-based program (BiteFinder). In the AI-IOS-corrected subgroup, the same AI-based program was used to correct the occlusal collisions of the articulated specimens obtained in the IOS-subgroup. A reverse engineering program (Geomagic Wrap) was used to calculate 36 interlandmark measurements on the digitized articulated casts (control) and each articulated specimen. Two-way ANOVA and pairwise multiple comparison Tukey tests were used to analyze trueness (α=.05). The Levene and pairwise multiple comparison Wilcoxon rank tests were used to analyze precision (α=.05).

RESULTS

Significant trueness discrepancies among the groups (P<.001) and subgroups (P<.001) were found, with a significant interaction group×subgroup (P<.001). The Levene test showed significant precision discrepancies among the groups (P<.001) and subgroups (P=.005). The TRIOS4 and iTero groups obtained better trueness and lower precision than the i700 and PrimeScan systems. Additionally, the AI-articulated subgroup showed worse trueness and precision than the IOS and AI-IOS-corrected subgroups. The AI-based program improved the MIP trueness of the scans articulated by using the iTero and PrimeScan systems but reduced the MIP trueness of the articulated scans obtained by using the TRIOS4 and i700.

CONCLUSIONS

The trueness and precision of the maxillomandibular relationship was impacted by the IOS system and program used to locate the MIP.

Effect of storage temperature on the dimensional stability of DLP printed casts

STATEMENT OF PROBLEM

Despite studies focusing on the accuracy and dimensional stability of additive manufacturing, research on the impact of storage conditions on these properties of 3-dimensional (3D) printed objects is lacking.

PURPOSE

The purpose of this in vitro study was to investigate the influence of storage temperature on the dimensional stability of digital light processing (DLP) printed casts and to determine how different locations in printed casts react differently.

MATERIAL AND METHODS

A completely dentate maxillary typodont model was digitized with a desktop laser scanner. The typodont was subsequently modified with a software program by adding cuboids with a side length of 3 mm on both maxillary central incisors, first molars, and second molars. The file was saved in the standard tessellation language (STL) format. The modified digitized typodont was then processed through the DLP technology printing process with a desktop DLP printer and photopolymerizing resin. The casts were printed 32 times and stored in sealed plastic bags, shielded from light, and subjected to 4 different temperature conditions (-20 °C, 4 °C, 20 °C, and 37 °C, n=8 each). The cuboids on the central incisors were labeled as the P1 group, first molars as the P2 group, and second molars as the P3 group. The distance between the cuboids was measured 5 times, with results recorded immediately after cast production and at 1, 2, 3, 5, 7, 14, and 28 days after. Repeated analysis of variance (ANOVA) and the Tukey honestly significant difference (HSD) test were used to compare the recorded values among the groups (α=.05).

RESULTS

In the P1 group, the casts stored at -20 °C exhibited the smallest overall size change, with a mean ±standard deviation volume of 99.42 ±0.04% compared with the original casts after 28 days of storage. This was followed by the casts stored at 4 °C, 20 °C, and 37 °C, with remaining volumes of 99.39 ±0.06% (P=.139), 99.14 ±0.08% (P<.001), and 98.96 ±0.03% (P<.001), respectively. For the P2 and P3 groups, casts stored at 4 °C retained the most volume at 99.82 ±0.01%, whereas those stored at -20 °C, 20 °C, and 37 °C underwent greater changes, with remaining volumes of 99.66 ±0.03%, 100.32 ±0.02%, and 100.44 ±0.02%, respectively (P<.001). The P3 group exhibited a similar trend to that of the P2 group, with the casts stored at 4 °C remaining closest to the original dimensions at 99.86 ±0.02%, while casts stored at -20 °C showed 99.73 ±0.03% of the original volume and those stored at 20 °C and 37 °C expanded with volumes of 100.37 ±0.03% and 100.48 ±0.03%, respectively (P<.001).

CONCLUSIONS

DLP printed casts stored at 4 °C exhibited the greatest overall dimensional stability, followed sequentially by those stored at -20 °C, 20 °C, and 37 °C. Additionally, the study confirmed that the posterior and anterior teeth regions of DLP printed casts respond differently to different storage temperatures.

In vitro study of the accuracy and efficiency of wireless intraoral scanners at various battery levels

OBJECTIVES

To determine the trueness and precision of 2 wireless intraoral scanners (IOSs) under various battery levels, and assess scanning efficiency.

METHODS

A maxillary cast with 4 metal spheres attached was fabricated. Two wireless IOSs (TRIOS 3 and TRIOS 4) were evaluated under 3 battery levels (1-30%, 31-60%, and 61-100%; n = 30). Six horizontal distances and 1 vertical distance were measured between 4 spherical centers and 1 generated plane. The distance deviations were determined with a coordinate-measuring machine data set. Kruskal-Wallis and Levene tests were used to analyze trueness and precision. Scan time and the number of three-dimensional (3D) images captured were analyzed by using a 2-way analysis of variance.

RESULTS

In terms of trueness and precision, no significant differences were found at various battery levels over the majority of the measured distances. TRIOS 4 demonstrated better trueness than TRIOS 3 for cross-arch scan. The 61-100% battery level resulted in the shortest scan time and the least number of 3D images captured (p < 0.001). Scan time and number of 3D images captured were strongly correlated for TRIOS 3 (r = 0.66) and TRIOS 4 (r = 0.89).

CONCLUSIONS

Changes in battery level had no impact on the trueness and precision of TRIOS 3 and TRIOS 4. High battery level IOSs resulted in faster scans and fewer 3D images captured with less storage space. TRIOS 4 scanned faster, captured fewer images, and demonstrated better trueness than TRIOS 3.

CLINICAL SIGNIFICANCE

Although all battery levels of wireless IOSs provide comparable trueness and precision, a wireless IOS with a high battery level is more time efficient than one with a low battery level in complete-arch scan.

In Vitro Trueness and Precision of Intraoral Scanners in a Four-Implant Complete-Arch Model

(1) Background: New intraoral (IOS) and laboratory scanners appear in the market and their trueness and precision have not been compared. (2) Methods: Seven IOS and two laboratory scanners were used to scan a mandibular edentulous model with four parallel internal hexagon implant analogues and PEEK scan bodies. Digital models in Standard Tessellation Language (STL) were created. The master model with the scan bodies was scanned (×10) with a computerized numerical control 3D Coordinate Measuring Machine (CMM). The short (distances of adjacent scan posts) and long distances (distances of the scan posts with non-adjacent sites in the arch) among the centroids of the four analogues were calculated using CMM special software. Trueness (comparisons with the master model) and precision (intragroup comparisons) were statistically compared with ANOVA, chi-square and Tukey tests. (3) Results: Laboratory scanners had the best trueness and precision compared to all IOSs for long distances. Only iTero (Align Technologies Inc., Milpitas, CA, USA) had comparable trueness with one laboratory scanner in short and long distances. For short distances, CS3600 (Carestream Health, Inc., Rochester, NY, USA), Omnicam, Primescan (Sirona Dental Sys-tems GmbH, Bens-heim, Germany) and TRIOS 4 (3Shape A/S, Copen-hagen, Denmark) had similar trueness to one laboratory scanner. From those, only Omnicam and Primescan had similar precision as the same laboratory scanner. Most IOSs seem to work better for smaller distances and are less precise in cross-arch distances. (4) Conclusions: The laboratory scanners showed significantly higher trueness and precision than all IOSs tested for the long-distance group; for the short distance, some IOSs were not different in trueness and precision than the laboratory scanners.

Novel method to delineate palatal rugae and assess their complexity using fractal analysis

Palatal rugae constitute significant morphological landmarks, with wide clinical applications in forensics, insertion of mini-screws, and superimposition. Their morphology has been studied mainly with indices relevant to their qualitative characteristics. The present paper aims at presenting a new quantitative method to evaluate their complexity, by means of box-counting fractal dimension analysis, and to investigate its inter- and intra-rater reliability. Twenty maxillary plaster models were scanned for the needs of this study. A sequence of steps, including cropping of the mesh, ball pivoting, distance mapping and fractal dimension analysis, performed with Viewbox 4 software, was followed. Box-counting fractal dimensions were calculated as a measure of rugae's complexity. Inter- and intra-rater reliability were investigated, using Bland-Altman analysis. Fractal dimensions ranged from 1.274 to 1.491 (average: 1.412). Bland-Altman analysis of inter- and intra-examiner reliability demonstrated that the 95% limits of agreement ranged from - 0.012 to 0.011 and from - 0.004 to 0.004, respectively. The method is reliable and can be applied in research and forensics. It offers comprehensive evaluation of the rugae's complexity and a complete set of information about their outlines and height profiles, with minimum user intervention.

Accuracy of photogrammetry, intraoral scanning, and conventional impression techniques for complete-arch implant rehabilitation: an in vitro comparative study

Background

To compare the accuracy of photogrammetry, intraoral scanning and conventional impression techniques for complete-arch implant rehabilitation.

Methods

A master cast containing 6 implant abutment replicas was fabricated. Group PG: digital impressions were taken 10 times using a photogrammetry system; Group IOS: intraoral scanning was performed to fabricate 10 digital impressions; Group CNV: splinted open-tray impression technique was used to fabricate 10 definitive casts. The master cast and conventional definitive casts were digitized with a laboratory reference scanner. For all STL files obtained, scan bodies were converted to implant abutment replicas using a digital library. The accuracy of a digitizer was defined by 2 main parameters, trueness and precision. "Trueness" was used to describe the deviation between test files and reference file, and "precision" was used to describe the closeness between test files. Then, the trueness and precision of three impression techniques were evaluated and statistically compared (α = 0.05).

Results

The median trueness was 24.45, 43.45 and 28.70 μm for group PG, IOS and CNV; Group PG gave more accurate trueness than group IOS (P < 0.001) and group CNV (P = 0.033), group CNV showed more accurate trueness than group IOS (P = 0.033). The median precision was 2.00, 36.00 and 29.40 μm for group PG, IOS and CNV; Group PG gave more accurate precision than group IOS (P < 0.001) and group CNV (P < 0.001), group CNV showed more accurate precision than IOS (P = 0.002).

Conclusions

For complete-arch implant rehabilitation, the photogrammetry system showed the best accuracy of all the impression techniques evaluated, followed by the conventional impression technique, and the intraoral scanner provided the least accuracy.

A Comparative Evaluation of Abrasion Resistance of Three Commercially Available Type IV Dental Stone, Dried using Three Different Drying Techniques - An In vitro Study

Background:

The microwave technique of drying dental stone to achieve improved hardness and strength has been suggested in recent years. However, its effect on the wear properties of dental stone has not been thoroughly examined.

Aim:

The present study was conducted in vitro to determine the abrasion resistance of three commercially available Type IV dental stones using three different drying techniques.

Materials and Methods:

A total of 180 samples were prepared from 3 Type IV dental stones; namely Eliterock, Zhermack (Italy), Kalrock, Kalabhai industries (India), and Gyprock (Rajkot, India). Samples were subjected to drying in open air for 2 h, hot air oven at a temp of 230°C for 1 h and microwave oven for 5 min at 900Watts. Abrasion resistance was determined using a customized metallic abrasion resistance tester.

Results:

Microwave oven drying produced samples with increased abrasion resistance values when compared to samples dried in hot air oven and air-dried specimens. Eliterock showed significantly higher mean abrasion resistance values followed by Kalrock and Gyprock.

Conclusion:

Drying type IV dental stone in a microwave oven at 900W for 5 min increased the abrasion resistance within short time.

The Effect of Different Additives on the Hydration and Gelation Properties of Composite Dental Gypsum

Dental mold gypsum materials require fine powder, appropriate liquidity, fast curing, and easy-to-perform clinical operations. They require low linear expansion coefficient and high strength, reflecting the master model and facilitating demolding. In this article, the suitable accelerators and reinforcing agents were selected as additives to modify dental gypsum. The main experimental methods used were to compare the trends of linear expansion coefficients of several commercially available dental gypsum products over 72 h and to observe the cross-sectional microstructure of cured bodies before and after dental gypsum modification using scanning electron microscopy. By adjusting the application of additives, the linear expansion coefficient of dental gypsum decreased from 0.26% to 0.06%, while the flexural strength increased from 6.7 MPa to 7.4 MPa at 2 h. Formulated samples showed good stability and gelation properties with linear expansion completed within 12 h. It is indicated that the performance of dental gypsum materials can be improved by adding additives and nanomaterials, which provided a good reference for clinical preparation of high-precision dental prosthesis.

Methods of mandibular condyle position and rotation center used for orthognathic surgery planning: a systematic review

We aimed to evaluate whether there is a consensus among bi- (2D) and three-dimensional (3D) evaluations of mandible condyle position and its rotation center. Also, if this data can be replicated in orthognathic surgery planning. The survey was carried out on the major databases (PubMed, SCOPUS, Embase, Cochrane). Human or human bio models evaluations in 2D or 3D of mandibular condylar position concerning its fossa and rotational axis for orthognathic surgery planning were eligible. The heterogeneity of the studies and uncertainties in methodological biases did not allow us to identify the superiority of 2D or 3D methodology in determination of the condylar rotational axis. There is a lot of divergences in the definition of occlusal relationships among dental specialties. Although there was no consensus regarding condylar position in relation to the fossa, the most reported axis of rotation was positioned posterior-inferior. Weak scientific evidence and divergences in dental vocabulary shows the need for clinical studies with more accurate and transparent methodological design to standardize concepts. Despite we cannot affirm, we can suggest that the centric relation (CR) is not the condylar position when clinically manipulated in the posterior superior direction. This condylar position is the retruded contact position (RCt) while CR is the functional position of the condyle. In this way, the orthognathic surgery has two occlusal relationships during planning and execution. The ideal axis of rotation for orthognathic surgery planning must be fixed, permit individualization for each condyle and be reproducible. The 2D planning is obsolete as cannot provide all the necessary tools for an accurate planning.

Effect of additive manufacturing process and storage condition on the dimensional accuracy and stability of 3D-printed dental casts

STATEMENT OF PROBLEM

Additively manufactured dental casts are gaining popularity as the digital workflow is adopted in dentistry. However, studies on their dimensional accuracy and stability under different storage conditions in the dental laboratory are lacking.

PURPOSE

The purpose of this in vitro study was to compare the effects of different additive manufacturing processes and storage conditions on the dimensional accuracy and stability of 3D-printed dental casts.

MATERIAL AND METHODS

A completely dentate maxillary typodont model was digitized 10 times with a dental laboratory laser scanner, and the standard tessellation language (STL) files were used to manufacture 3D-printed diagnostic casts with the digital light projection (DLP) 3D printer (Asiga MAX) and material jetting (MJ) 3D printer (ProJet 3510 DPPro). Twenty DLP-printed and 20 MJ-printed diagnostic casts were digitized within 24 hours of production. Subsequently, all 3D-printed diagnostic casts were stored for 3 months, either in closed laboratory boxes or in dental laboratory open-face plastic containers with direct exposure to full-spectrum balanced light. After 3-month storage, all 40 3D-printed casts were digitized again. All scanned files were compared with the corresponding STL files in a surface-matching software program. The dimensional accuracy was measured and compared by the root mean square (RMS, in μm). Repeated measures analysis of variance (ANOVA) was used to compare RMS values among the variables, and the Tukey honestly significant difference (HSD) test was used for post hoc multiple comparisons (α=.05).

RESULTS

The casts produced from the DLP 3D printer had a significantly higher mean ±standard deviation RMS of 153.7 ±25.4 μm than those produced with the MJ 3D printer with RMS of 134.1 ±16.0 μm (P<.001). The storage condition (box storage versus light exposure) did not affect the accuracy of the DLP-printed casts (P=.615) or the MJ-printed casts (P=.999). When comparing all 3D-printed casts after 3-month storage, group DLP-3M-Lit had the highest mean ±standard deviation RMS of 163.0 ±26.5 μm, and group MJ-3M-Box had the lowest RMS of 132.8 ±16.9 μm. The DLP-printed casts stored under light exposure were significantly less accurate than the MJ-printed casts stored in the box (P=.048). DLP-printed casts stored under light exposure showed significant surface color change under visual inspection.

CONCLUSIONS

The MJ 3D printer produced more accurate 3D-printed dental casts than the DLP 3D printer. After 3-month storage, the DLP-printed casts stored under light exposure were the least accurate, and the MJ-printed casts stored without light exposure were the most accurate. The surface color change of DLP-printed casts stored under light exposure after 3-month storage was evident.

Dimensional accuracy of microcomputed tomography-scanned half-arch impressions

STATEMENT OF PROBLEM

Accuracy in impression making may be enhanced by digitizing the physical impression directly and thereby be unhampered by errors introduced by gypsum casts.

PURPOSE

The purpose of this in vitro study was to compare the dimensional accuracy of microcomputed tomography (micro-CT) scans of impressions with that of optical scans of impressions and gypsum casts.

MATERIAL AND METHODS

A titanium maxillary cast with 3 metrology-grade ruby spheres in place of 3 teeth was used as a reference. Sphere 1 (S1) to sphere 2 (S2) distance (S1-S2) was 25.036 mm, and sphere 1 (S1) to sphere 3 (S3) distance (S1-S3) was 41.846 mm. Half-arch impressions were made of the titanium cast using polyvinyl siloxane impression material with a 1-step 2-phase technique. The polyvinyl siloxane impressions were then micro-CT scanned and optically scanned, and the resulting stone casts were also optically scanned. Scans from the 3 groups-CT scanning of impressions (CT), optical scanning of impressions (OP), and optical scanning of stone casts (SC)-were used to measure the distances between the 3 ruby spheres and were compared with the reference titanium model. The Wilcoxon signed-rank test for matched pairs was used to compare the groups (α=.01).

RESULTS

For the distance of 25.036 mm, S1-S2 distance, CT scans of impressions (CT) showed an error of 20 ±20 μm, whereas optical scans of stone casts (SC) showed an error of 0 ±20 μm. At a distance of 41.846 mm, S1-S3 distance, CT showed an error of 0 ±40 μm, whereas SC showed an error of -40 ±40 μm. The difference in error between measurements at both distances was statistically significant (P<.01). The group of optical scans of impressions (OP) had to be excluded because of missing data and deformed features on the scan.

CONCLUSIONS

Although optically scanned stone models are more dimensionally accurate than micro-CT scanned impressions at a 25.036-mm distance, at a distance of 41.846 mm, micro-CT scanned impressions showed less error than optically scanned stone models. Micro-CT scanning of half-arch impressions is a viable method of digitizing a physical impression of dental structures and capturing data about the patient's oral structures. A digital image obtained by micro-CT scanning is more accurate than that obtained by optical scans of stone casts for long-span restorations.

The sensitivity of digital intraoral scanners at measuring early erosive wear

OBJECTIVES

To investigate the sensitivity of intraoral scanners to quantitatively detect early erosive tooth wear.

METHODS

Natural buccal enamel samples were mounted in acrylic and scanned at baseline with an intraoral scanner (3 M True Definition Scanner, 3 M, USA). Samples were then exposed to 0.3% citric acid pH 3.2 at intervals of 10 min up to a total of 120 min and scanned after each exposure resulting in analysis of 13 datapoints per sample. Each scan was aligned with the baseline and data points super-imposed using an iterative closest point (ICP) algorithm on the acrylic surfaces (Geomagic Control Software, 3Dsystems, Darmstadt, Germany). Wear was measured using maximum profile loss, average profile loss and volume change. Data were normally distributed and Pearson correlations between erosion time and wear measurements assessed.

RESULTS

After each 10-minute exposure until 120 min, maximum profile loss (μm) increased from 33.4 to 72.8 μm, average profile loss from 9.1 to 18.6 μm. Wear correlated with increasing acid exposure for both maximum profile loss wear (r = 0.877 p < 0.001) and average profile loss (r = 0.663 p = 0.019) respectively. Volume measurements were inconsistent at this level of wear.

CONCLUSIONS

Using scan data obtained from the intra oral scanners (IOS), increasing step height changes were observed with increasing exposures to acid. This study indicates there is potential of scans taken with an IOS to be used to detect early erosive tooth wear. However, precision was low suggesting limitations for minimal changes.

CLINICAL SIGNIFICANCE

Although sub-visual wear was detected by intra-oral scanners on natural enamel surfaces, the accuracy was not sufficient to reliably diagnose that wear had occurred and interpretation of measurements should be done with caution. However, these results may be promising for detecting wear at more advanced stages.

Performance and perception of dental students using three intraoral CAD/CAM scanners for full-arch scanning

PURPOSE

To assess the average full-arch scanning time, perception and likelihood of future adoption of technology by final-year dental students using three different Computer-Aided Design/Computer-Aided Manufacturing (CAD/CAM) intraoral scanning systems.

METHODS

Final-year undergraduate Dental Students (FDS), with no prior experience of intraoral scanning, full-arch scanned (IOS) a mannequin head-mounted model under supervision. Three scanning systems were used, TRIOS Colour (TRIOS); True Definition (TDef); and CEREC AC OmniCam (CEREC). Thereafter, FDS completed a questionnaire to assess their perception of IOS. Data were analysed by Generalized Estimating Equations, Fisher's exact tests and logistic regression.

RESULTS

Forty-nine FDS participated. Average full arch IOS time varied significantly (p<0.001) among the TRIOS, CEREC, and TDef, at 4min (n=48), 4min 42s (n=33), and 7min 32s (n=41) respectively. IOS using the TRIOS was significantly (p<0.001) the quickest, while TDef was the slowest (p<0.001). Seventy-one percent of FDS had positive overall IOS experience. FDS who reported intraoral scanning was timesaving compared with conventional impressions were more likely to adopt the technology after graduation (odds ratio (OR)=11.91, 95% confidence interval (CI)=2.56-55.45, p=0.002).

CONCLUSIONS

Intraoral scanning performance of novice users varied significantly and was dependent on the scanning system used. The questionnaire showed that the overall IOS experience was positive amongst FDS. The perception of time-saving, when using IOS versus conventional impression methods, determined the likelihood of future adoption of the technology.

The addition of silica nanoparticles on the mechanical properties of dental stone

STATEMENT OF PROBLEM

The current application of nanotechnology in dentistry is limited to nanoparticles incorporated into adhesive systems and composite resins. Dental stone is a widely used material, and the incorporation of silica nanoparticles is still unexplored.

PURPOSE

The purpose of this in vitro study was to evaluate the mechanical properties of dental stone after the addition of silica nanoparticles in different concentrations.

MATERIAL AND METHODS

A total of 180 specimens were prepared, 90 for each dental stone (Durone and Fuji Rock). For the control group (CG), no silica particles were added, while test group TGnI had silica nanoparticles added to 1 wt%, and test group TGnV had silica nanoparticles added to 5 wt%. The roughness, diametral tensile strength (DTS), and compressive strength were measured 24 hours after the start of spatulation.

RESULTS

The mean roughness values for Durone were 0.55, 0.36, and 0.28 μm for CG, TGnI, and TGnV; for Fuji Rock, the mean roughness values were 0.47 for CG, 0.31 for TGnI, and 0.35 μm for TGnV. The mean DTS values for Durone were 6.0, 5.1, and 5.0 MPa for CG, TGnI, and TGnV, respectively, and for Fuji Rock, the mean DTS values were 6.4, 5.2, and 4.5 MPa for CG, TGnI, and TGnV, respectively. The mean compressive strength values for Durone were 35.4, 32.7, and 32.4 MPa for CG, TGnI, and TGnV, respectively, and for Fuji Rock, the mean compressive strength values were 42.9, 31.2, and 29.8 MPa for CG, TGnI, and TGnV respectively.

CONCLUSIONS

Surface roughness was statistically lower for the Durone and Fuji Rock stones (P<.001) when silica nanoparticles were added. The addition of silica nanoparticles did not significantly affect the DTS and compressive strength of Durone compared with CG (P>.05) but did affect the DTS of Fuji Rock when 5 wt% was added and the compressive strength in both concentrations (P<.05).

Analysis of the Mechanical Behavior and Surface Rugosity of Different Dental Die Materials

AIM

This work evaluated the mechanical and surface behavior of different die materials. The studied materials are polyurethane resin Exakto-Form (Bredent), Gypsum type IV, Fuji Rock EP (Gc), and Durone (Dentsply).

MATERIALS AND METHODS

Two metallic matrices molded in polyvinyl siloxane provided 30 cylindrical test specimens for the diametral compression test and 30 hemispherical test specimens for the surface rugosity test. The cylindrical test specimens were submitted to tests of diametral compression strength using a DL2000 universal assay machine, with a load cell of 2000 Kgf and constant speed of 1 mm/min connected to the software. Kruskal-Wallis and Dunn's nonparametric tests were used to analyze the results. The hemispheres were submitted to the surface rugosity assay using a SJ201-P rugosimeter with a sensitivity of 300 μm, speed of 0.5 mm/s, and cut-off of 0.8 mm, and the readings were taken on the convex surface of the test specimens and metallic matrix. Results were analyzed using with Fisher's least significant differences test (LSD) and Dunnett's test.

RESULTS

Kruskal-Wallis test showed significant difference between die materials for diametral compression strength (P = 0.002). Dunn's test showed significantly higher values for modified polyurethane resin (Exakto-Form). The gypsum type IV, which did not significantly differ regarding diametral compression strength, showed 34.0% (Durone) and 42.7% (Fuji Rock) lower values in comparison to Exakto-Form.

CONCLUSION

Within the parameters adopted in this study, it is possible to conclude that Exakto-Form polyurethane resin showed higher resistance to compression and was closer to the metallic matrix rugosity, and, along with the gypsum type IV Durone, showed better reproducibility of details relative to the Fuji Rock.

Accuracy of Gypsum Casts after Different Impression Techniques and Double Pouring

This study evaluated the accuracy of gypsum casts after different impression techniques and double pouring. Ten patients were selected and for each one it was obtained 5 partial putty/wash impressions with vinyl polysiloxane (VPS) material from teeth #13 to #16 with partial metal stock trays. The following techniques were performed: (1) one-step; two-step relief with: (2) PVC film; (3) slow-speed tungsten carbide bur and scalpel blade, (4) small movements of the tray and (5) without relief—negative control. The impressions were disinfected with 0.5% sodium hypochlorite for 10 minutes and stored during 110 and 230 minutes for the first and second pouring, respectively, with type IV gypsum. Three intra-oral lateral photographs of each patient were taken using a tripod and a customized radiographic positioner. The images were imported into ImageJ software and the total area of the buccal surface from teeth #13 to #16 was measured. A 4.0% coefficient of variance was criterion for using these measurements as Baseline values. The casts were photographed and analyzed using the same standardization for the clinical images. The area (mm²) obtained from the difference between the measurements of each gypsum cast and the Baseline value of the respective patient were calculated and analyzed by repeated-measures two way-ANOVA and Mauchly’s Sphericity test (α = 0.05). No significant effect was observed for Impression technique (P = 0.23), Second pouring (P = 0.99) and their interaction (P = 0.25). The impression techniques and double pouring did not influence the accuracy of the gypsum casts.

Effect of dental technician disparities on the 3-dimensional accuracy of definitive casts

STATEMENT OF PROBLEM

Studies that evaluated the effect of dental technician disparities on the accuracy of presectioned and postsectioned definitive casts are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the accuracy of presectioned and postsectioned definitive casts fabricated by different dental technicians by using a 3-dimensional computer-aided measurement method.

MATERIAL AND METHODS

An arch-shaped metal master model consisting of 5 abutments resembling prepared mandibular incisors, canines, and first molars and with a 6-degree total angle of convergence was designed and fabricated by computer-aided design and computer-aided manufacturing (CAD-CAM) technology. Complete arch impressions were made (N=110) from the master model, using polyvinyl siloxane (PVS) and delivered to 11 dental technicians. Each technician fabricated 10 definitive casts with dental stone, and the obtained casts were numbered. All casts were sectioned, and removable dies were obtained. The master model and the presectioned and postsectioned definitive casts were digitized with an extraoral scanner, and the virtual master model and virtual presectioned and postsectioned definitive casts were obtained. All definitive casts were compared with the master model by using computer-aided measurements, and the 3-dimensional accuracy of the definitive casts was determined with best fit alignment and represented in color-coded maps. Differences were analyzed using univariate analyses of variance, and the Tukey honest significant differences post hoc tests were used for multiple comparisons (α=.05).

RESULTS

The accuracy of presectioned and postsectioned definitive casts was significantly affected by dental technician disparities (P<.001). The largest dimensional changes were detected in the anterior abutments of both of the definitive casts. The changes mostly occurred in the mesiodistal dimension (P<.001).

CONCLUSIONS

Within the limitations of this in vitro study, the accuracy of presectioned and postsectioned definitive casts is susceptible to dental technician differences.

Accuracy of Intraoral Digital Impressions for Whole Upper Jaws, Including Full Dentitions and Palatal Soft Tissues

Intraoral digital impressions have been stated to meet the clinical requirements for some teeth-supported restorations, though fewer evidences were proposed for larger scanning range. The aim of this study was to compare the accuracy (trueness and precision) of intraoral digital impressions for whole upper jaws, including the full dentitions and palatal soft tissues, as well as to determine the effect of different palatal vault height or arch width on accuracy of intraoral digital impressions. Thirty-two volunteers were divided into three groups according to the palatal vault height or arch width. Each volunteer received three scans with TRIOS intraoral scanner and one conventional impression of whole upper jaw. Three-dimensional (3D) images digitized from conventional gypsum casts by a laboratory scanner were chose as the reference models. All datasets were imported to a specific software program for 3D analysis by "best fit alignment" and "3D compare" process. Color-coded deviation maps showed qualitative visualization of the deviations. For the digital impressions for palatal soft tissues, trueness was (130.54±33.95)μm and precision was (55.26±11.21)μm. For the digital impressions for upper full dentitions, trueness was (80.01±17.78)μm and precision was (59.52±11.29)μm. Larger deviations were found between intraoral digital impressions and conventional impressions in the areas of palatal soft tissues than that in the areas of full dentitions (p<0.001). Precision of digital impressions for palatal soft tissues was slightly better than that for full dentitions (p = 0.049). There was no significant effect of palatal vault height on accuracy of digital impressions for palatal soft tissues (p>0.05), but arch width was found to have a significant effect on precision of intraoral digital impressions for full dentitions (p = 0.016). A linear correlation was found between arch width and precision of digital impressions for whole upper jaws (r = 0.326, p = 0.034 for palatal soft tissues and r = 0.485, p = 0.002 for full dentitions). It was feasible to use the intraoral scanner to obtain digital impressions for whole upper jaws. Wider dental arch contributed to lower precision of an intraoral digital impression. It should be confirmed in further studies that whether accuracy of digital impressions for whole upper jaws is clinically acceptable.

The influence of postpouring time on the roughness, compressive strength, and diametric tensile strength of dental stone

STATEMENT OF PROBLEM

The optimum time after pouring a dental impression before removing the dental cast is unknown with regard to the strength and roughness of the stone. Setting times and the commercial products used are important variables.

PURPOSE

The purpose of this study was to evaluate the effect of postpouring time on the surface roughness, compressive strength, and diametric tensile strength of Type IV dental stone.

MATERIAL AND METHODS

A total of 270 specimens were prepared from 3 commercial brands of dental stone (Durone, Fuji Rock, and Tuff Rock). Surface roughness, compressive strength, and diametric tensile strength were assessed at 1 hour, 24 hours, and 7 days after pouring. Specimens 6 mm in diameter and 3 mm in height were produced for roughness and diametric tensile strength tests. Specimens 3 mm in diameter and 6 mm in height were used to measure compressive strength. The results were analyzed with the general linear model and Tukey honestly significant difference test (α=.05).

RESULTS

The surface roughness measured for the different types of dental stone tested varied from 0.3 μm (Durone, 1 hour) to 0.64 μm (Tuff Rock, 7 days). The diametric tensile strength ranged from 3.94 MPa (Tuff Rock, 1 hour) to 9.20 MPa (Durone, 7 days). The compressive strength varied from 26.67 MPa (Durone, 1 hour) to 65.14 MPa (Fuji Rock, 7 days).

CONCLUSIONS

Surface roughness (P=.005), diametric tensile strength (P=.001), and compressive strength (P=.001) increased significantly with time after pouring. The commercial brand used affected roughness (P=.001), diametric tensile strength (P=.004), and compressive strength (P=.001). Tuff Rock exhibited the highest surface roughness. The highest diametric tensile strength values were recorded for Durone and Fuji Rock. Fuji Rock exhibited the highest compressive strength.

Three-dimensional repositioning accuracy of semiadjustable articulator cast mounting systems

STATEMENT OF PROBLEM

In spite of its importance in prosthesis precision and quality, the 3-dimensional repositioning accuracy of cast mounting systems has not been reported in detail.

PURPOSE

The purpose of this study was to quantify the 3-dimensional repositioning accuracy of 6 selected cast mounting systems. Five magnetic mounting systems were compared with a conventional screw-on system.

MATERIAL AND METHODS

Six systems on 3 semiadjustable articulators were evaluated: Denar Mark II with conventional screw-on mounting plates (DENSCR) and magnetic mounting system with converter plates (DENCON); Denar Mark 330 with in-built magnetic mounting system (DENMAG) and disposable mounting plates; and Artex CP with blue (ARTBLU), white (ARTWHI), and black (ARTBLA) magnetic mounting plates. Test casts with 3 high-precision ceramic ball bearings at the mandibular central incisor (Point I) and the right and left second molar (Point R; Point L) positions were mounted on 5 mounting plates (n=5) for all 6 systems. Each cast was repositioned 10 times by 4 operators in random order. Nine linear (Ix, Iy, Iz; Rx, Ry, Rz; Lx, Ly, Lz) and 3 angular (anteroposterior, mediolateral, twisting) displacements were measured with a coordinate measuring machine. The mean standard deviations of the linear and angular displacements defined repositioning accuracy.

RESULTS

Anteroposterior linear repositioning accuracy ranged from 23.8 ±3.7 μm (DENCON) to 4.9 ±3.2 μm (DENSCR). Mediolateral linear repositioning accuracy ranged from 46.0 ±8.0 μm (DENCON) to 3.7 ±1.5 μm (ARTBLU), and vertical linear repositioning accuracy ranged from 7.2 ±9.6 μm (DENMAG) to 1.5 ±0.9 μm (ARTBLU). Anteroposterior angular repositioning accuracy ranged from 0.0084 ±0.0080 degrees (DENCON) to 0.0020 ±0.0006 degrees (ARTBLU), and mediolateral angular repositioning accuracy ranged from 0.0120 ±0.0111 degrees (ARTWHI) to 0.0027 ±0.0008 degrees (ARTBLU). Twisting angular repositioning accuracy ranged from 0.0419 ±0.0176 degrees (DENCON) to 0.0042 ±0.0038 degrees (ARTBLA). One-way ANOVA found significant differences (P<.05) among all systems for Iy, Ry, Lx, Ly, and twisting.

CONCLUSIONS

Generally, vertical linear displacements were less likely to reach the threshold of clinical detectability compared with anteroposterior or mediolateral linear displacements. The overall repositioning accuracy of DENSCR was comparable with 4 magnetic mounting systems (DENMAG, ARTBLU, ARTWHI, ARTBLA). DENCON exhibited the worst repositioning accuracy for Iy, Ry, Lx, Ly, and twisting.